Compared to their terrigenous counterparts, carbonate shell accumulations have until recently been relatively little studied to determine either descriptive or genetic classifications of shell bed types, the preservation potential of each type, or their relative ability to preserve community-level information. A partial classification of Paleozoic carbonate shell-rich soft sediment accumulations is proposed using sedimentation patterns in the Lebanon limestone of the Stones River Group. Paleoecological information preserved therein is then contrasted by shell bed type. The Lebanon represents typical Ordovician shallow to moderate subtidal carbonate shelf deposits in outcrops flanking the Nashville Dome and peritidal deposits in the Sequatchie Anticline of Eastern Tennessee; shell beds alternate with shell poor sediments (micrites, wackestones and diagenetically enhanced dolomites and clay-rich partings).

None of the analyzed shell beds was strictly biological in origin; most are sedimentological although >10% are combined sedimentological/diagenetic. While the majority are single simple shell beds, >20% are amalgamated. All are thin (1 shell to 15 cm) stringers that pinch and swell showing poor lateral continuity (outcrop scale, tens to hundreds of meters) likely enhanced by burial dissolution. These shell beds differ greatly in fabric (packing/sorting), clast composition, taphonomic signature, and intensity of time averaging; thus community information retrieval is biased in predictable patterns. Virtually no shell beds show common shell dissolution or encrustation from long-term sediment surface exposure or hardground formation. Five major categories of accumulation are herein proposed using a DESCRIPTIVE, non-genetic terminology modified from previous works of DJD, as well as a Genetic interpretation for each. These are easily distinguished in the field and are also discriminated by Q-mode cluster analysis.

Categories include, in decreasing frequency of occurrence: 1. SHELL GRAVELS; Storm/“event” beds: Sharp bases; poorly sorted coarse basal bioclasts and/or intraclasts, often with no preferred orientation; clasts fine upward to comminuted shell material and micrite. Horizontal platy brachiopods often cap the beds. High diversity and a wide range in shell alteration is represented, from whole unaltered brachiopods to minor abraded fragments, indicating extreme time averaging and poor resolution of short-term community dynamics. 2. COMMINUTED SHELLY LS; Current/ripple concentrations: Small tidal channel fill and discrete ripple trough accumulations are composed of cross-stratified bioclastic deposits with local concentrations of rip-ups. Beds are not graded; typically clasts are abraded, rounded and concordant with cross-beds. Intense time averaging and mixing of discrete communities is inferred due to continual reworking in these background deposits. 3. SHELL/CEMENT LS; Early cementation beds: Intense early diagenetic alteration is inferred due to red discoloration and rapid intergranular cementation; some beds show diagenetic micritic rinds. Beds may be brecciated and show deep burial stylolitization cutting bioclasts and cement. They may represent zones of preferred early cementation rather than a change in shell accumulation rate. Many shells from some beds show little postmortem alteration; these units may preserve much of the original community structure. 4. DENSE SHELL PAVEMENTS; Subtidal surficial pavements: Single layers of shells, commonly concave down, overlie mudstones/wackestones with no basal erosion. No obrution deposits were noted. Bioclasts are typically disarticulated and reoriented, but are not substantially abraded, broken, or dissolved. Diversity is low. Only minor temporal and lateral community mixing with small environmental fluctuation is indicated. 5. VERTICALLY IMBRICATE SHELLY LS; High energy beach zones: Platy whole and major fragments of brachiopods are deposited in low diversity, high angle imbricate beds. Less postmortem reworking and time averaging is evident compared to types 1 and 2.

Thus, the most common (physically reworked) shell bed types show the most intense loss of short-term paleocommunity information. There are surprisingly few insitu community pavements or obligate long-term accumulations. This pattern differs from some described Ordovician carbonates, which may contain common community beds or hardgrounds/hiatal accumulations. This implies a relatively low rate of net sediment accumulation on a shallow, periodically wave swept shelf, and no major flooding surfaces or other indications of significant sea level change. Delineation of the sequence stratigraphic position of these carbonates is enhanced from this type of integrated community/biostratinomic analysis.

The taphonomy of birds can be investigated with actualistic studies complemented by reviewing Konversat Lagerstätten such as Messel, Green River and Solnhofen.

Two field sites were chosen in southern Florida: 1, a freshwater (16–23 ppt salinity) environment in which biogenic carbonate muds were being deposited and 2, a marine (30–34 ppt salinity) environment in which pyritous carbonate muds were being deposited. Ninety-six specimens (36 genera, 40 species) were used in this study (these were obtained from a wildlife centre where they died of natural causes). Experiments were set up in both marine and freshwater sites in the following categories: large protected, unprotected; small protected, unprotected. Protected specimens were placed in metal cages coated with small mesh (1.5mm2) nylon netting.

The specimens were allowed to degrade under natural conditions. The following variables were recorded daily over a seventy day period: air and water temperature, humidity, rainfall, wind and current speed and direction, salinity, dissolved oxygen content, pH, and water depth. Specimens from each of the eight categories were sampled at day 1, 4, 7, 11, 28, 56, and 70.

Scavengers play a major role in the early taphonomic processes. Unprotected specimens were rapidly removed from the study area by large predators such as alligators (Alligator mississippiensis) and American crocodiles (Crocodylus actus), and Turkey vultures (Cathartes aura). Even protected specimens were prone to attack by more “intelligent” large scavengers such as racoons. Smaller predators include crayfish in the freshwater site and the carnivorous gastropods (Crown conch) in the marine environment. The Crown conch was observed to be a voracious feeder and large numbers rapidly strip all flesh from any carcass within reach of the bottom.

Decay proceeds rapidly in the warm waters of the field sites. Within the carcasses temperatures approach optimum bacterial temperatures and large bacterial colonies form within muscle blocks after only one day. The initial decay of the muscle fibres is also rapid (one day) as the muscle myofibrils start to break into short lengths and the myoseptum starts to disintegrate, and has totally disappeared after seven to fourteen days (depending on the initial mass of the bird).

From graphs showing plots of percentage weight loss (weight loss as a percentage of original weight) versus time decay can be seen to follow an exponential curve ie. most rapid decay occurs early (as soft tissues decay) then weight loss slows down (after 10 days for small specimens and 28 days for large specimens) as by this time nearly all but the most resistant soft tissues have decayed and the weight loss is due to the removal of skeletal matter to the sedimentary record. Feathers are resistant to the initial stages of decay and the primary and secondary feathers remain attached to the wing bones for up to twenty-eight days even when the soft tissues have been totally removed.

The results of the decay experiments have provided directly comparable specimens to those that can be found within the fossil record. This comparison of fossil and modern analogues allows a series of taphonomic thresholds to be defined in the fossilisation of birds.

The importance of hydrologic processes in determining where and how a shell will be deposited is widely acknowledged, but few actualistic studies of these processes have been conducted. Additional knowledge of how the hydrologic regime influences the post-mortem distribution, orientation, and burial of modern shells can provide valuable paleoecological insights.

For the purposes of biostratinomy, single and articulated shells of Macoma nasuta and Clinocardium sp. were studied in False Bay, a semicircular inlet located on the west coast of San Juan Island, WA. Dead shells of these species were the most numerous and conspicuous skeletal elements present on the tidal flats. Transects were used to quantify the valves' natural distribution, orientation and depth of burial. Shell concentrations were significantly greater toward shore and decreased toward the center of the bay. The majority of these valves were articulated (56.4%) and oriented in the convex-up attitude (71.7%).

Tides and waves were the bay's dominant hydrologic forces. Spring low tides (maximum range of -0.8 m to 2.6 m) leave most of the bay subaerially exposed. During periods of immersion, waves from the Straits of Juan de Fuca underwent refraction, diffraction, and shoaling as they moved into False Bay. This influence was evidenced in the concentric sand bars which average 100 m long, 20 m wide and 0.5 m high. Painted and numbered valves were used to determine the effects of waves and tides. Shells were place in m2 areas both in a tidal channel and on a sand bar at low tide and then left for 1–2 tidal cycles. Recovery rates of shells ranged from 76.7% to 93.3%. Regardless of initial attitude, the majority were found in a convex-up attitude; convex-up valves remained in that orientation (89.8% – 97.7%) while those initially convex-down were reoriented to the convex-up position (75% – 86%). These findings confirmed that the convex-up position is the most hydrodynamically stable.

The most interesting aspect of this study was the nature of valve transport. Valves placed in the tidal channel moved less than one meter while those on the sand bar showed a strong bimodal distribution: shells moved either less than 2 m or distances ranging from 10 to greater than 119 m. The long range transport was unexpected; it was caused by the flotation, under calm meteorological conditions, of subaerially exposed convex-down shells on the incoming tide. This mode of transport moved the valves considerably greater distances than either saltation or traction in bedload. Shell flotation was not correlated to valve size, handedness, nor species.

A combination of shape and form, mode of preservation, and degree of variation makes the strophomenoids one of the more difficult groups of brachiopods to study taxonomically. In turn, taxonomic confusion may explain why the strophomenoids have not been used to the same extent as other groups of brachiopods as a basis for biostratigraphic classification and correlation, and for elucidating biogeographic provincialism. Such conclusions certainly seem warranted following a detailed investigation of the strophomenoids present in the Late Ordovician-Early Silurian carbonate sequence of Anticosti Island, Quebec.

The abundance and superb preservation of Anticosti strophomenoids permit a thorough analysis of external and internal features and the high degree of variation that some of these exhibit. Serial sections are critical to reconstructing the interiors of articulated specimens, establishing taxonomic relationships among discrete valves, and exposing developmental changes in shell structure. When subject to such detailed treatment, at least seventeen genera and twenty-seven species of strophomenoids can be securely identified. Variation among these taxa is such that some features - shape, convexity, ornamentation, and outline of muscle field - hitherto depended upon for taxonomic purposes, have little value in this respect. Other features - pattern of pseudopuncta, form of foramen, pseudodeltidium, chilidium, cardinal process, teeth, dental plates, and socket plates, and presence of ridges and septa bounding and dividing the muscle field - are demonstrably more reliable.

The Ordovician-Silurian boundary in the Anticosti sequence is broadly characterized by change from a plectambonitid-rafinesquinid-strophomenid fauna in the Vaureal Formation (Ashgill), through a plectambonitid-leptaenid-stropheodontid-Fardenia fauna in the Ellis Bay Formation (uppermost Ashgill), to a leptaenid-stropheodontid-Fardenia fauna in the Becscie to Chicotte formations (Llandovery). Considerable overlap occurs between Ordovician and Silurian taxa. The oldest known chonetid and the oldest stropheodontid on Anticosti Island occur in the Vaureal Formation. Plectambonitids and strophomenids are rare in the late Llandovery Jupiter Formation.

Taking a more rigorous biostratigraphical approach, however, distribution of the twenty-seven well-constrained species allows numerous sequential biozones of different type (assemblage, range, overlapping range) to be recognized, up to six of them in the Ashgill section alone. Some zones are distinguished by cosmopolitan species, others by species known from basins well removed from the Anticosti Basin, others again by species seemingly endemic to the Anticosti Basin. These replacements point to a changing pattern of faunal provincialism as Late Ordovician gave way to Early Silurian time. In the Ordovician portion of the section in particular, the biostratigraphic refinement of the potential strophomenoid zones exceeds that of such other brachiopod groups as rhynchonellids or of conodonts.

IGCP 203 - Permo-Triassic events of eastern Tethys and their intercontinental correlation - focussed on the Permian-Triassic boundary sequences and in particular there was a consensus that the distinctive biological changes were associated with strong sea-level and tectonic change, strong volcanic activity and a harsh climate. These factors were connected with an important change in the environment and with the exception perhaps of the climate, reflected deep-seated changes within the earth. The project also resulted in improving the physical understanding of the sequences and their biostratigraphy and correlation.

IGCP 272 was developed, and was approved in 1988, to apply these results to understanding the Late Palaeozoic and Early Mesozoic and was focussed on the Pacific as integration around this region seemed to offer especially fruitful possibilities.

Working group meetings up to the end of 1991 have been held in Australia (Newcastle and Hobart), New Zealand (Dunedin), South America (Sao Paulo and Buenos Aires) and North America (Washington). Meetings are planned in North America, Japan, Eastern Siberia or Thailand and western Europe (France-Spain-Austria).

Special cooperation has developed with the Carboniferous, Permian and Triassic Subcommissions of IUGS and with IGCP 214 - Global Bio-events. Using the more exact time correlations developed it has now been possible to show that major geological and biological events (of different levels of significance) are associated with major boundaries already recognized in the World Standard Stratigraphical Time Scale. These comprise the Carboniferous-Permian, the mid-Permian (twofold subdivision, the Permian-Triassic (already recognized in earlier work), the Lower-Middle and Middle-Upper Triassic and the Triassic-Jurassic boundaries.

A special achievement of the project has been to show the similar significance of the Midian-Dzhulfian boundary within the Upper Permian but corresponding closely to the traditional Lower-Upper Permian of China and the Middle-Upper Permian of Japan.

Although there are also other events at levels which have not been investigated by the project, those outlined all seem to reflect important changes within the earth.

Llandovery (Lower Silurian) echinoderm faunas are uncommon, an observation which has important implications for our understanding of the patterns of evolution and extinction over the Ordovician/Silurian boundary interval. For example, only two crinoid faunas of Rhuddanian or Rhuddanian+Aeronian age have so far been described, both from North America (Cataract Group, Ontario; Brassfield Formation, Ohio). A third echinoderm fauna of Rhuddanian age is now recognized from the Gasworks Mudstones (=upper Haverford Mudstone Formation) and, less certainly, the Gasworks Sandstone Formation of Haverfordwest, Dyfed, southwest Wales. Recent fieldwork has failed to relocate the precise horizon that produced this fauna and the taxa discussed herein are all based on specimens in the Turnbull Collection of the Sedgwick Museum, Cambridge. There is no published analysis of this fauna, but Ramsbottom, in his Ph.D. thesis, identified Pisocrinus sp., Macrostylocrinus sp. and Dimerocrinites sp. from this horizon.

A disarticulated thecal plate has been identified as the rhombiferan Homocystites? sp., confirming that the cheirocrinids survived the end Ordovician extinction. This is only the second British Llandovery cystoid. All other specimens are crinoids. Crowns of calceocrinid disparids are assigned to two species of Calceocrinus (=“Pisocrinus sp.” of Ramsbottom). A dendrocrinid cladid is interpreted as a smmoth-cupped Dendrocrinus? A unique internal mould is a monobathrid, possibly Macrostylocrinus. Distinctive petaloid columnals of Floricolumnus (col.) sp. cf. F. girvanensis Donovan and Clark, possibly derived from a rhodocrinitid diplobathrid, are congeneric with ossicles from the Newlands Formation of southwest Scotland (latest Rhuddanian-earliest Aeronian) and the Brassfield Formation of Ohio (‘Bead Bed’). A new species of rhodocrinitid diplobathrid (=“Dimerocrinites sp.” of Ramsbottom) has low infrabasals just apparent in lateral view; a moderately bowl-shaped dorsal cup; prominent ray ridges; 2, 3 or 5 plates, respectively, in the first three tiers of interprimibrachials; and uniserial arms that branch isotomously once and heterotomously thereafter. Two further crinoid species are indeterminate. At the familial level, this fauna shows strong similarities with coeval, but more diverse, crinoid assemblages from North America.

Paleozoic acritarch and marine phytoplankton associations clearly interpret paleoenvironments within marine shelf and oceanic depositional areas. Marginal marine sediments are characterized by low diversity acritarch assemblages, while shelf areas contain a higher diversity of forms. Areas with significant terrestrial runoff tend to have higher phytoplankton abundance together with terrestrial palynomorphs in contrast to restricted circulation carbonate shelf areas with distinctive low abundance acritarch associations. Deep water basinal and oceanic areas with low phytoplankton nutrient availability are characterized by very low diversity acritarch associations of moderate to very low abundance. Within the Paleozoic, changes in relative sea level are indicated by the record of a series of acritarch associations reflecting changing depositional environments comparable to depositional sequences and parasequences.

The stratigraphic record in Panama and Costa Rica preserves the biologic and climatic changes associated with the formation of a major barrier to marine migration and ocean circulation. Creating a high resolution temporal framework within which stratigraphic sections found on the Isthmus can be interpreted is fundamental to our understanding the history and importance of these units.

The Isthmus contains rich marine macro- and microfaunas and floras on both the Pacific and Atlantic margins. Planktic foraminifers and calcareous nannofossils are common and often well preserved. Preliminary analysis of these fossils reveals a rich sedimentary record spanning the Late Miocene to Pleistocene. Multivariate statistical analyses of these assemblages provide environmental estimates. Unfortunately, traditional methods of biostratigraphy are limited in their ability to create a high resolution temporal framework for the region. For example, a majority of deposits analyzed can be placed in planktic foraminiferal zone N19 (early Pliocene). In order to answer paleobiologic and paleoclimatic questions one requires more precise correlations between sections and some indication of duration of sedimentation represented by various sections.

In an attempt to overcome the shortcomings of traditional biostratigraphic methods, the Graphic Correlation method has been applied to selected sequences on the Central American Isthmus. Graphic correlation (GC) is a procedure by which two sequences can be compared and correlated using a wide variety of stratigraphic information simultaneously. A GC model of late Neogene planktic foraminifer, calcareous nannofossil, and paleomagnetic reversal events has been produced through compositing of more than 26 deep sea cores and ocean margin sequences. Following routine GC procedures the positions of all fossil first and last occurrences from a number of sections on the Caribbean and Pacific sides of the Central American Isthmus (Panama and Costa Rica) have been recorded. These sections have been correlated to the GC model and hence, to each other, providing a temporal framework for the Isthmus units.

Selected sections were then correlated to other sequences such as near-by deep sea cores which have been analyzed for sea surface temperature and salinity to gain a better understanding of the overall paleoceanographic development of the region between 5 and 2 Ma. For example, correlation of units on the Caribbean side of the Isthmus with DSDP Site 502 indicates little to no change in sea surface temperatures during the entire time the Isthmus was reaching closure. Mid-to-high latitude sites exhibit amplification of warming with increasing latitude. The shoaling Isthmus, while having negligible effects on tropical marine temperatures, was responsible for increased meridional heat transport which resulted in a North Atlantic warming about 3 Ma. A general model for paleoceanographic changes during the time of closure will be discussed.

Scleractinian and rugose corals demonstrate a broad environmental distribution and have been documented in strata reflecting deposition from high-energy, nearshore reefal to low-energy basinal settings. Both clades have a relatively high diversity of representatives which live(d) at great depths. While deep-water scleractinian coral banks are well-documented, commonly the deep-water representatives of both clades are the small, solitary, and often delicate forms. In order to determine the nature of diversification of these deep-water forms the paleoenvironments of the earliest Rugosa and representatives of extant deep-water scleractinian families were determined. Environmental patterns of the subsequentdiversification of the Rugosa and scleractinian sub-order Caryophylliina were also documented. Environmental information was determined from independent sedimentological data.

The earliest reported Rugosa is Lambeophyllum from the Chazyan Crown Point Limestone (VT, U.S.A.), which was deposited in an nearshore/inner shelf setting. Subsequentto this occurrence, rugosans appear nearly simultaneously in North America, Australia, Europe and China. However, common Lambeophyllum, within the Blackriverian Orwell Limestone (NY, U.S.A), appearsto be the earliest of these occurrences. The Orwell is, likewise interpreted to be shallow water in origin. After their initial appearance in an onshore environment, the Rugosa rapidly expand offshore. While Middle Ordovician Rugosaare of low diversity (1 genus at a given locality), by the end of the Blackriverian they are found in middle and outer shelf settings.

Nearly all representatives of families of extant scleractinians now living in deep-water (>200’) also first occur in an onshore environment - primarily the inner shelf. The caryophylliids, the most speciousdeep-water coral clade, first appear in Toarcian age inner shelf strata and soon after occur in outer shelf deposits. However, occurrences of high diversities of caryophylliids (generic diversity greater than 4 at a given locality) are confined to inner shelf settings until the Cretaceous when generic diversities of 2 or more are common in the outer shelf. In the Tertiary, high diversities of caryophylliids are generally restricted to slope and deep basin settings, a pattern which characterises their modern distribution.

Both rugose and scleractinian corals expand offshore at low diversities within 5 million years of their first appearance and thus, demonstrate environmental diversification before taxonomic diversification.

The Savannah River Site (SRS) has produced and disposed of a variety of potentially hazardous materials since the early 1950's; as a result, ground water is contaminated at several locations on the site. In 1991, the U.S. Geological Survey, in cooperation with the U.S. Department of Energy and the Georgia Department of Natural Resources, began a 6-year study to determine if ground water is flowing from aquifers in South Carolina beneath the Savannah River and into aquifers in Georgia and, if not, under what conditions such flow could occur. A conceptual model based on physical data and a digital ground-water-flow model will be developed to better understand the ground-water-flow system in the study area. Biostratigraphic interpretations will be used to help define the hydrogeologic framework for the conceptual and digital models.

The SRS is located in the South Carolina Coastal Plain on the eastern side of the Savannah River, approximately 100 miles upriver from the Atlantic Ocean. In this area, aquifers of Late Cretaceous and Tertiary age are recharged by precipitation. The age and stratigraphic correlation of sediments in the study area have been controversial because existing fossil evidence is sparse, lithologies of adjacent units are commonly similar, and facies changes occur in relatively short distances. These three factors have also complicated understanding of the ground-water-flow system, because clay and silt confining units are more discontinuous updip; therefore identification of ground-water flow paths and delineation of aquifers and confining units are difficult. Detailed biostratigraphy, using marine and nonmarine fossils, is essential to understanding the depositional history of the region and to determining the complex three-dimensional relations of stratigraphic and hydrogeologic units needed for accurate conceptual and ground-water-flow models.

Development of the hydrogeologic framework will require data on the geologic, hydrologic, and water-quality characteristics of coastal plain sediments. To provide these data, clusters of seven to ten wells will be constructed at each of seven sites. At each site, a continuous core will be collected from land surface to basement rock, and monitor wells will be installed in each water-bearing zone. The first three cluster sites are located in Georgia along an updip-downdip transect parallel to the Savannah River. The southernmost of the three sites will serve as a biostratigraphic and lithostratigraphic reference section because it will have the thickest section of sediments and will contain marine facies in which a greater abundance of fossil evidence can be expected. Paleoenvironmental data will help predict the continuity of confining units between cluster sites.

The paleoecology of deep-sea, benthic, macroinvertebrate communities is largely confined to the trace fossil record. While a few taxa have preservable hard parts, most of the deep-sea macrofauna are unpreservable as body fossils below the aragonite or calcite compensation depths. The ichnologic record provides important synecologic information regarding the behavioral diversity and endobenthic habitat partitioning of at least some community members.

The deep-sea trace fossil record is strongly influenced by sediment composition (biogenic calcite vs. terrigenous clay), sedimentation regime (pelagic vs. turbidite deposition) and bioturbation history (continuous vs. discontinuous burrowing). These influences are directly reflected in the ichnofabric, or biogenic sedimentary fabric.

Ichnofabrics of deep-sea sediments can shed light on the ecologic relationships of the infaunal community (trophic and tiering relationships), occupation of the sea floor by successive and different communities (deciphered from the different trace fossil suites in a composite ichnofabric), stability and firmness of the sedimentary substrate (revealed by burrow distinctness and deformation), interstitial oxygen conditions below the sea floor (determined from the abundance and preservation state of deposit-feeding burrows, such as Chondrites and Zoophycos), and effects of bioturbation patterns on early diagenetic processes (differential cementation and mineralization).

The sedimentary habitat of the ancient deep-sea floor changes through time via compaction, dewatering, cementation and secondary mineralization. The benthos that inhabit this changing habitat likewise change according to their differing requirements for burrowing and endobenthic feeding. The resulting ichnofabric reflects a successive occupation of the sea floor by different types of organisms, ranging from shallow burrowers to deep burrowers to hard-substrate borers. Composite ichnofabrics thus can reveal a complex sequence of ecologic and diagenetic events.

The tiered structure of infaunal communities in late Cretaceous and early Tertiary shelf-sea chalks is well-known, and because of their pelagic depositional aspect, these situations provide good analogues in outcrop for truly deep-sea environments. In the European and North American chalks, deeply emplaced fodinichnia (Thalassinoides, Chondrites and Zoophycos) typically are superimposed upon shallowly emplaced fodinichnia and pascichnia (Planolites and Teichichnus). Tracks and trails of epifaunal animals certainly were produced at the sediment-water interface, but they are not preserved. Very similar ichnofabrics occur in late Cretaceous and early Tertiary pelagic carbonates in New Zealand, where composite ichnofabrics reveal at least five main phases of occupation of the substrate by burrowers and borers. Multiple generations of Thalassinoides include both burrows and borings, each produced at different stages in the development of a major regional unconformity.

Deep-sea pelagic deposits (in kilometers of water) represent a continuous accretion of the sea floor during sediment accumulation, accompanied by a continuous vertical shift of a tiered endobenthic community of burrowers that does not change appreciably over short time intervals. In partial contrast, shelf-sea pelagic deposits (in hundreds of meters of water) are affected more directly by short-term changes in bathymetry, salinity and oxygenation. The response of benthic communities to environmental shifts at the sea floor, therefore, is more pronounced in shelf-sea than in deep-sea settings.

Three successive coral faunas that are involved in the Ordovician-Silurian mass extinction and recovery occur in latest Ordovician (Richmondian-Gamachian) to earliest Silurian (early Llandovery; Rhuddanian) strata of the east-central United States. The Richmondian fauna comprises typical cratonic North American Late Ordovician corals. In the Cincinnati Arch region, these belong to the Richmond Province and include massive stauriids (e.g., Favistina), sarcinulids (e.g., Foerstephyllum, Calapoecia), and common tetradiids. In the upper Mississippi Valley region, corals belong to the Red River-Stony Mountain Province and include the streptelasmatid Salvadorea. The disappearance of typical Ordovician-type coral faunas from the interior of eastern North America was related to habitat loss resulting from progradation of the Queenston delta and regression of the epeiric sea during a major glacio-eustatic drop in the late Richmondian.

The succeeding fauna of Gamachian to early Rhuddanian age represents the Edgewood Province. The solitary rugosan Streptelasma is dominant; colonial rugosans are rare and are all fasciculate. The principal tabulates are Paleofavosites, Propora, and Halysites; sarcinulids are absent. Rare tetradiids (Rhabdotetradium) are among the youngest representatives worldwide of an important Ordovician order. The Edgewood fauna includes first occurrences of typical Silurian taxa: the earliest North American halysitine (Halysites), the oldest definite plasmoporid (Plasmopora), and the earliest known pycnostylid (Pycnostylus). The striking difference between Richmondian and Edgewood faunas in the east-central United States reflects, at least in part, a hiatus between Richmondian and Gamachian deposition. Corals were introduced to the Edgewood Province from the continental margin, or were derived from forms previously restricted to the continental margin. This occurred during minor transgressions from the south, as sea level fluctuated during a regressive phase corresponding to the Gamachian glacial maximum. Immigration was evidently related to shifts of suitable habitat areas during a time of depressed temperatures. Edgewood corals dispersed farther northward during the early phase of the major latest Gamachian to Early Llandovery transgression associated with deglaciation.

Corals are uncommon in late Rhuddanian strata immediately above those containing the Edgewood fauna. This Silurian fauna includes the solitary rugosans Rhegmaphyllum, Dinophyllum, Dalmanophyllum, and Cyathactis?, which were not derived from Edgewood taxa. Colonial rugosans are absent. The tabulates belong to Paleofavosites, Propora, and Halysites, the dominant colonial genera in the Edgewood fauna. At least some of the species were likely derived from Edgewood forms; others may have been introduced from elsewhere, or perhaps were derived from species in other areas. A slight stratigraphic overlap of several Edgewood and Silurian species is known at one locality, but the faunal change is otherwise abrupt. The changeover from Edgewood to Silurian faunas took place as water depth and temperature were generally increasing during the Rhuddanian. However, corals of the Silurian fauna appear above intraformational channels in one area and above unconformities or formational boundaries elsewhere, suggesting that the change occurred during an intervening regressive event. It is inferred that as areas in the east-central United States became inhospitable, geographic ranges of Edgewood corals were reduced. Most species became extinct; some colonial corals apparently underwent rapid evolution, probably in small populations. The descendants dispersed and new immigrants arrived as suitable habitat areas expanded when the Early Llandovery transgression resumed. A few Edgewood colonial species survived for a short time, evidently in local refugia. Unlike the colonial corals, all solitary forms known from the Silurian assemblage were immigrants. Corals of the Silurian assemblage probably favored somewhat deeper water than those of the Edgewood Assemblage.

The gastropod superfamily Subulitoidea first appeared during the Early-Middle Ordovician gastropod radiation, seemingly from within the pleurotomarid family Lophospiridea, and persisted with low diversity and generally low abundance through the Paleozoic. One species survived the end-Permian mass extinction, but like many other Paleozoic remnants, the clade became extinct in the mid-Triassic. Many members of the clade are homeomorphic with later ‘neogastropods' and have frequently been fingered as the ancestors of these later, predatory gastropods. There is however, no direct evidence for an ancestor-descendent relationship. Addressing this possibility and understanding of the systematics and evolutionary history of the clade has been complicated by relatively simple shell form and apparent paucity of shell characters. The strength of the morphological and probable ecologic similarities between subulitids and ‘neogastropods' raises the question why this clade was unable to capitalize on their position as perhaps the only predatory gastropods during the Paleozoic. Such questions of evolutionary history are best addressed within the context of a combination of morphometric and phylogenetic analyses which may resolve the systematic questions and reveal something of the evolutionary relationships of the clade.

Morphometric analyses were performed on some 40 specimens covering the 13 described genera (and several undescribed forms). Both linear and angular measurements of external shell form and internal structure from axial thin sections were measured and apertures were analyzed using elliptical Fourier analysis (EFA). The number of specimens analyzed was intentionally limited because of difficulties obtaining specimens with sufficient preservation of the aperture. The results demonstrate the necessity, for this clade at least, of including a more complex description of apertural morphology than simple maximum length and width. Principle component analyses of the EFA data distinguishes complexity of the columellar folds along the first axis and basal rounding along the second - both biologically meaningful aspects of apertural form. Moreover, the occupation of a taxon-specific apertural space defined by the PCA increases through the Paleozoic. Further, the analyses suggest that the two traditionally recognized subfamilies of the Subulitidae (Ordovician-Devonian and Devonian-Triassic) each exhibit increased variance in the occupation of morphologic space, but additional data is required to confirm this pattern and determine if any temporal trends exist.

Analyzing patterns of occupation of morphologic space requires a rigorously constructed phylogeny. A cladistic (parsimony) analysis of the superfamily was performed using 16 taxa and over 30 discrete morphologic characters. The resulting cladograms were plotted within the taxon-specific morphospaces produced by the morphometric analyses.

The fossil record is commonly (but not universally) invoked as an historical record with which to test evolutionary scenarios. The process by which this takes place involves the recognition of patterns of taxa in a temporal framework. The patterns are in turn interpreted as the result of some evolutionary mechanism. We submit that if the fossil record is to be a tool in evolutionary studies, the use of appropriately-defined higher taxa can be consistent with the objective of recognizing patterns from which evolutionary events can be inferred.

We implemented a study to monitor the ecological diversity of “families” of dinosaurs through the last 2.2 million years of the Cretaceous in the terrestrial sediments of the Hell Creek Formation in eastern Montana. We concluded, using the Shannon index and rarefaction as monitors, that at the “family” level, the ecological diversity of dinosaurs remained constant.

We suspect that the taxa we designated as “families” did not branch ancestrally at equivalent points in their respective phylogenies. Nevertheless, each is a monophyletic group, established and united by synapomorphies. We therefore measured and tracked the relative proportions of monophyletic groups through sequential time slices of the latest Cretaceous. We interpreted this as a measure of ecological diversity.

The phylogenetic methods that were used to define the extinct “families” in our study are epistemologically indistinguishable from methods that are used to establish monophyletic fossil groups at any taxonomic level, including the lowest levels. Why should special significance be attributed to a taxonomic level (i.e., species) that is obtained by means no different from those used to obtain the other levels?

Use of the fossil record in evolutionary reconstruction requires the recognition of patterns, and the attribution of evolutionary mechanisms to those patterns. It is unlikely that selection acts on units other than populations which arguably, are not even taxa. Recognition of historical patterns rather than causality or process, therefore, may be the unique province of the stratigraphic record.

Estuaries were important sites of deposition throughout most of the Pennsylvanian in the Midcontinent. Modern estuaries typically occur within flooded river valleys where marine and fresh waters mix. Characteristic estuarine circulation results in locally high rates of deposition of muddy sediment that can lead to good preservation of fossils. Several Pennsylvanian conservat-Lagerstätten are best interpreted as having formed within ancient estuaries. Three types of estuarine deposits have been identified. Type 1 estuarine systems are large-scale transgressive systems that start with fluvial sands overlying an erosional surface. This is overlain successively by middle-estuarine laminated mudstone, and finally marine mudstone and shale. Well-preserved fossils occur in laminated mudstones and siltstones. This sequence may include within in it type 3 estuarine Lagerstätten. An example is the Douglas Group (Missourian, Kansas).

Type 2 estuarine Lagerstätten consist of thin estuarine deposits confined to narrow paleochannels. This includes the Garnett (Missourian, Kansas) and Hamilton (Virgilian, Kansas) deposits, both of which contain articulated vertebrates and well-preserved plants. Both channels are filled with mixed siliciclastic and carbonate sediments. Fine grained facies from which the best fossils are recovered in both contain evidence of tidal deposition, although tidal rhythmicity is best developed in the Hamilton channel. Plant assemblages in both are dominated by the conifer Walchia, probably indicating a relatively dry climate.

Type 3 estuarine Lagerstätten consist of thick gray-shale wedges that overlie coals. The best-known example is the Francis Creek Shale (Desmoinesian, Illinois). A relatively wet climate is indicated by abundant fern and seed-fern foliage. Laminations in shale facies commonly show well-developed tidal rhythmicity. A typical stratigraphic succession starts with laminated shale overlying coal. This grades upwards into flaser and lenticular bedding to ripple and then large-scale cross-bedded sandstone. Upright trees rooted in the coal indicate rapid burial. Well-preserved fossils are recovered from early-diagenetic siderite concretions from the laminated shale.

Preservation of fossils is best in laminated mudstones deposited in middle-estuarine environments where conditions are ideal for good preservation. In all cases so far studied the zones of best preservation are well laminated and have sparse (if any) burrows and sessile benthic fossils. Most of the well-preserved organisms are terrestrial, nektonic, or at least mobile. Brackish and fluctuating salinities restricted scavenging and burrowing organisms that may scatter skeletons. High turbidity and deposition rate may have further discouraged many organisms. Matching bedding rhythmicity with tidal cycles allows calculation of depositional rates of 1 cm or more of compacted sediment per 2-week neap-spring tidal cycle. This is consistent with the high rates of deposition known from modern tidal environments. High depositional rates assured that any organism that fell to the sea floor was buried in a few hours to a few days. Once buried anoxic conditions established around decaying carcasses may have led to early mineralization.

Palynological analysis of stratigraphically-controlled samples from a number of localities in the Succor Creek area of the Oregon-Idaho boundary, the Stinking Water flora of eastern Oregon, and the Trapper Creek flora of southern Idaho has proved to be a valuable interpretive tool in the study of these mid-Miocene plant assemblages. Models derived from analysis of the Succor Creek data suggest: 1) paleotopographic trends, 2) patterns of distribution of major forest elements, 3) the role of disturbance and succession, and 4) limits for paleoclimatic reconstruction. These have proved consistent with patterns of megafossil representation at Succor Creek and both megafossil and palynological data at Stinking Water and Trapper Creek. Such models also appear useful in the refinement of ecological affinities of a number of megafossil taxa which occur in these and other Neogene assemblages throughout the northern Intermountain region.

Some taxa are quite specific in their affinities, both in terms of vegetational maturity and elevational zonation. Species of Abies, Picea, Pseudotsuga, Thuja and Tsuga appear characteristic of ecologically mature forests at somewhat higher elevations. Such forests are rare at Stinking Water, are best developed in the southern part of the Succor Creek region, and represent the “climax” forests at Trapper Creek. In contrast, broad-leaved taxa, including species of Castanea, Castanopsis, Nyssa, and most Quercus, are reliable indicators of ecologically mature, lower elevation forests.

The ecological significance of a number of mixed-mesophytic taxa, including species of Carya, Juglans, Liquidambar, Pterocarya, Sassafras, Tilia, Ulmus, and Zelkova, is ambiguous. Broad-leaved deciduous assemblages dominated by these plants occur as mid-seral recovery stages over a wide range of elevation from lowlands to higher slopes. Ecologically mature forests of these trees tend to be found only at intermediate elevations. At lower elevations they are largely, but not exclusively, replaced in later seral stages by the ecologically mature, low-elevation taxa noted previously; while at higher elevations they are replaced by conifers.

Some taxa, most notably Equisetum, Glyptostrobus, Osmunda, and Typha are restricted to very wet habitats, irrespective of elevation. The shade-intolerant Typha forms ephemeral marshes that are rapidly replaced by Glyptostrobus swamps. Lake margins (and riparian settings), over a wide elevational gradient, are characterized by thickets of Acer, Alnus, Arbutus, Populus, Quercus simulata, “Quercus” eoprinus, and Salix. Locally Sequoia occurs in upland settings (i.e. at Payette, Idaho), while Glyptostrobus is more common in lowlands (Stinking Water and northern Succor Creek localities), but can occur in lower frequencies at any paleoelevation. Some taxa, such as Acer medianum appear to be characteristic of mid-seral recovery stages in these wet habitats.

Two very different plate-tectonic models have been proposed to explain the development and emplacement of the Robert Mountains allochthon (RMA) onto the North America craton during the Late Devonian-Early Mississippian Antler Orogeny. In one model, the RMA represents a far-traveled accretionary prism that migrated eastwards over a west-dipping subduction zone. In the other, the eugeoclinal strata of the RMA were deposited on the continental rise of western North America within a closed back-arc basin. Siliciclastic sediments, especially quartz sandstones, compose much of the RMA, yet knowledge of their provenance is poor even though such knowledge is essential for evaluating the two plate-tectonic models.

We have recently obtained large collections of graptolites and conodonts from turbiditic quartz sandstones in the Lower Member of the Vinini Formation in the Roberts Mountains. These sandstones of lower Whiterockian age are correlative with the lower Antelope Valley Limestone that deposited on the western shelf of North America. The diverse graptolite fauna represents the oceanic isograptid fauna. However, it also includes pendent didymograptids and rooted dendroids that were restricted to shallow shelf seas. The dendroids (Cactograptus, Dendrograptus, Desmograptus, and Dictyonema) were benthic organisms, could not have lived in a deep marine setting, and are also common in shallow-water carbonate strata of western Utah. All specimens within the turbiditic quartz sandstones of the Vinini were broken before final deposition and burial, but specimens from Utah are generally complete. The diverse conodont fauna is virtually identical to that found in the lower Antelope Valley Limestone, as well as in coeval strata in western Utah. Although it includes a few deep (cold) water, cosmopolitan species, it is dominated by species that are otherwise known only from shallow water strata deposited on the North American craton.

We conclude that turbidity currents transported these exotic graptolites and conodonts down from the shelf and onto the rise along with the quartz sands in which they occur. Thus, the Whiterockian quartz sandstones in the Vinini Formation must have a North American provenance just as the fossils do. This is strong evidence that 1) the RMA is not exotic to North America, 2) the eugeoclinal strata of the RMA were deposited on the western continental rise of North America and on the eastern side of a back-arc basin, and 3) the RMA was thrust onto the western shelf of North America by closure of this back-arc basin.

Conical skeletal elements of various morphologies are a feature common to numerous Lower and Middle Cambrian organisms of problematic affinity, not to mention their occurrence in multiple extant metazoan phyla. In some cases these display helicospiral morphology, sometimes with dextral and sinistral morphs that may have been paired structures in a bilaterally symmetrical body plan. Such paired elements, including spines of coeloscleritophorans, appear to show a spicular substructure with some suggestion of spatial organization comparable to that of phyllotactic systems in vascular plants. These recurring structural themes raise old questions regarding the significance and mode of development of spiral forms and patterns in many organisms, both unicellular and multicellular.

Most recent work on phyllotaxis has interpreted patterns of spiral organization as emergent geometrical properties of systems controlled by local reaction-diffusion interactions around the developing plant axis, without recourse to any explicitly spiral process. The term “generative spiral,” for the pattern linking consecutively formed elements, has thus taken on a purely descriptive, rather than mechanistic, meaning. Likewise, helicospiral shells and comparable structures are generally assumed to reflect no truly spiral growth mechanism, but rather, the regular scaling and displacement of a fundamentally concentric, cone-within-cone, accretionary system. Explanations for the common appearance of such forms include the structural strength offered by adherent whorls (though many forms are evolute), and the simplicity of isometric growth (though departures from logarithmic spirals are common).

An alternative perspective was suggested initially by discovery of a higher order pattern in the phyllotactic systems of some conifers, wherein the handedness of the generative spiral reverses as each parent axis gives rise to daughters, through the full range of levels in the branching hierarchy. Although this may be explicable in conventional terms, it may also be interpreted as involving a spiral wave of activation passing rhythmically around the plant axis, at or within some critical distance of the apical meristem. Models for such phenomena are provided by several physical systems involving excitable media, the most well known of which is the Belousov-Zhabotinsky reaction, and by some biological systems, such as neural networks or aggregations of slime mold. At nearly the opposite end of the organismic realm, vertebrate teeth, most of which are subtly but fundamentally helicospiral in form, show features that also suggest rotating waves of activity. These include the common presence of an axial canal in the dentin underlying tooth cusps, which could represent the phase singularity of a rotating wave in the layer of odontoblasts responsible for dentin formation, and asymmetries in autoradiographic patterns associated with developing teeth. In such systems it may be generally true that the period of other physiological cycles that modulate secretory activity is not a simple multiple of the period of rotation of the spiral wave. This would result in a regular change in phase relationship, generating helicospiral form. Additional applications of this principle may illumine features as diverse as bovid horns and the handedness of supernumerary appendages in grafting experiments on insects and amphibians. Spiral waves in excitable media also have properties of symmetry and capacity for generating serial structure that make them intriguing candidates for involvement in even earlier stages of metazoan development.

The geographic distribution of taxa appears to affect their survivorship during both background and mass extinction. Direct paleontological evidence for this tendency is strong, but inevitably incomplete on a global scale due to extreme geographic variation in preservation and sampling. As a complementary approach to the relation between biogeography and extinction, we are modelling potential survivorship patterns using a global biogeographic database for Recent shallow (< 200 m) marine bivalve molluscs. To date, we have collected information on genera from 10 superfamilies: Arcacea, Limposacea, Mytilacea, Pinnacea, Pteriacea, Pectinacea, Carditacea, Cardiacea (including Tridacnacea), Tellinacea, and Veneracea. Although these superfamilies represent only one-fourth of all marine superfamilies, they include approximately 46 percent of the extant marine genera. We used species lists or monographs to disentangle many generic assignments, thus attaining uniformity of treatment at the generic level among 115 sites or regions. These faunas together represent all latitudinal zones, all oceans, and many oceanic islands and inland seas.

The expected latitudinal and inter-ocean diversity gradients are clearly seen in our data. Although high latitude faunas are consistently low in generic diversity, tropical bivalve faunas may have high, intermediate, or low generic diversities, mainly because of the relative impoverishment of Atlantic faunas and the low diversity of tropical island faunas relative to their continental shelf counterparts. Island faunas are dominated by cosmopolitans, underscoring the importance of dispersal in maintaining bivalve populations on oceanic islands.

We simulated extinction of bivalve faunas by “eliminating” genera restricted to particular latitudinal zones, oceans, continental shelves or oceanic islands. Because endemism at the generic level is low (despite today's high global thermal gradient and wide dispersal of continents), extinctions comparable to the K/T and P/Tr can be accomplished only through the annihilation of faunas in several latitudinal zones or oceans. Either today's fauna is more cosmopolitan than those of the past, or major mass extinctions required truly pervasive and profound environmental upheavals.

Calculations of “rates of evolution” have been applied to a variety of indicators of change within populations, species, or higher taxa. This has led to confusion about taxonomic and temporal scaling, particularly when rates are calculated for supposedly “equivalent” taxonomic ranks, or “higher-level” taxa that are not monophyletic groups. All calculations of rates of evolutionary change require accurate temporal calibration. Even in studies of molecular evolution that assume a “molecular clock”, the rate at which any clock ticks must be calibrated empirically by fossil data on the age of divergence of some taxa.

Molecular clock rates for all Mammalia generally have been calculated from the primate fossil record and phylogeny. However, rates of molecular evolution have been shown to vary both within and among different clades. Given a preference for a more rigorous system in which molecular divergence is not assumed to occur at a constant rate, the time of divergence should be determined directly for all clades in studies of molecular “rates of evolution”.

The mammalian order Carnivora is a monophyletic group widely cited in studies of evolutionary tempo, and mode. However, few of those rate studies have considered explicitly the roles of fossil taxa and rigorously tested phylogenies. For example, phylogenetic placement of early Cenozoic Carnivora (generally placed in the paraphyletic “stem-group” “Miacoidea”), relative to the two major clades of living Carnivora (Caniformia and Feliformia), profoundly influences estimates of the age of cladogenetic divergence for clades of living carnivorans. If all the taxa placed within the “Miacoidea” lie outside a restricted clade of Carnivora (defined as the most recent common ancestor of extant Carnivora, and all of its descendants), then the oldest Carnivora (“neocarnivorans”) are late Eocene (about 35–40 Ma). However, if miacid “miacoids” are caniforms and viverravid “miacoids” are feliforms, then the Caniformia/Feliformia (=Carnivora) clade is at least as old as the oldest “miacoid” (middle Paleocene, or >60 Ma). The implications for calculations of rates of evolution within Carnivora are obvious. Similarly, many fossil Carnivora taxa have been assigned to living families, although the phylogenetic relationships of both fossil and living taxa within most of these families has been poorly understood. This presentation will consider: 1) minimum estimates of clade divergence time, based on current hypotheses of carnivoran phylogeny (emphasizing placement of fossil taxa) and oldest occurrence of fossils within a clade or its sister group- traditional taxonomies both underestimate (e.g. Caniformia/Feliformia) and overestimate (e.g. some living families, such as Viverridae) clade divergence times; and 2) calculation of rates of evolution within Carnivora, focusing on taxonomic diversification and molecular divergence, comparison of rates calculated using traditional taxonomies and artificial “higher-taxa” categories versus those using phylogenetic clades (“unranked”), and the effects of fossil taxa.